VIP decelerates non-REM-REM cycles and modulates hormone secretion during sleep in men

Centrally administered vasoactive intestinal polypeptide (VIP) promotes rapid eye movement (REM) sleep in rats, rabbits, and cats. We studied the effect of 4 x 10 mu g VIP (expt 1, n = 7) and 4 x 50 mu g VIP (expt 2, n = 10) administered hourly as intravenous boluses between 2200 and 0100 on sleep electroencephalogram and secretion of plasma adrenocorticotropic hormone, cortisol, growth hormone, and prolactin in humans. In experiment 2, the sleep cycles were decelerated during the first three cycles because of increased duration of both REM and non-REM sleep periods, and there was a tendency to increased REM-to-non-REM ratios. With a low VIP dose, prolactin levels were decreased during the whole night, whereas, with a high dose, they were increased during the first half of the night. In experiment 2, the cortisol nadir was advanced, after midnight the serum cortisol levels were enhanced, and the growth hormone peak was blunted. It appears that VIP may have a phase-advancing effect on sleep cycles and cortisol secretion, possibly through actions that involve the suprachiasmatic nucleus.